The present invention relates generally to a vacuum system utilized for evacuating the space between at least two laminae of a laminated assembly and, in particular, to a vacuum ring construction which is utilized for de-airing a laminated glass assembly such as an automobile windshield, for example.
In the early stages of the automobile industry, single sheets of ordinary glass were employed as windshields. As it became evident that this type of windshield presented a considerable safety hazard, the single sheets of ordinary glass were replaced with single sheets of heat treated or tempered glass. Thereafter, laminated safety glass was developed to further reduce the severity of lacerative injuries. The use of laminated glass assemblies in automobile windshields greatly increased until today, when almost all automotive windshields are constructed of some type of laminated glass.
Typically, a laminated glass assembly of the type utilized in vehicle windshields consists of two sheets of glass bonded together with a thin plastic interlayer, such as a sheet of polyvinyl butyral, for example. In the event of an impact on the laminated glass windshield sufficient to break the glass, the plastic interlayer functions to bind the glass fragments together, thus reducing the risk of injury to a driver or a passenger as a result of flying glass or contact with the windshield. Recently, it has been found that the addition of a second plastic layer applied to the inner surface of the windshield further increases the effectiveness of the laminated glass. This second plastic layer has been called an anti-laceration shield. Also, it has been found that single sheets of glass having an anti-lacerative plastic layer applied to the inner surface of the glass can effectively function as a windshield or other type of safety window.
One of the problems in manufacturing laminated glass assemblies of the type described above is related to the assembling and bonding techniques utilized to produce a windshield having high optical qualities. Once the individual laminae of the laminated assembly have been assembled in a stacked arrangement, the individual laminae are pressed toward one another while the entire assembly is heated to a predetermined temperature to cause the intermediate layers of plastic material to soften and bond to the adjacent glass sheets. Typically, such an operation is performed in an autoclave. The autoclave includes a heated and pressurized chamber for receiving the stacked arrangement of individual laminae. The heated chamber of the autoclave can be sealed and pressurized, causing the individual laminae to be urged toward one another, while the increased temperature causes the plastic laminae to soften and bond to the adjacent glass laminae.
Prior to placing the stacked arrangement of individual laminae in an autoclave it has been found desirable to "de-air" the assembly by evacuating air spaces which may be present between the individual laminae. One method of de-airing a laminated glass assembly is to place the entire stack of individual laminae in a plastic bag and thereafter evacuate the bag. Another approach is to utilize a vacuum ring of the type disclosed in U.S. Pat. Nos. 2,948,645 and 3,074,466. These patents disclose a vacuum ring which is constructed of a flexible material and is provided with a channel formed therein for receiving the entire peripheral edge of the laminated glass assembly. The channel of the vacuum ring includes a recessed portion which is maintained in a spaced apart relationship with the entire peripheral edge of the glass assembly. This recessed portion defines a passageway which is coupled to a vacuum source. When the vacuum ring is mounted about the peripheral edge of the glass sheet, and coupled to the vacuum source, the vacuum removes the majority of the air spaces between the laminae.
In some instances, it is desirable to maintain the vacuum ring about the laminated assembly when the assembly is positioned within an autoclave, and to apply a vacuum to the assembly during at least a portion of the time when the assembly is heated and pressurized by the autoclave. However, one of the problems with such an approach is that during such an operation, the softened plastic layers are typically forced outwardly past the marginal edges of the glass sheets and into the recessed portion of the vacuum ring. This tends to reduce the thickness of the plastic layers around the marginal edges of the glass, and consequently produces undesirable optical distortion in those areas.